WO2024260494A1 - Sodium ion battery, method for producing a sodium ion battery and use of a sodium ion battery - Google Patents

Abstract

The invention relates to a sodium ion battery comprising a cathode which has a composite cathode active material, and an anode which has an anode active material. The composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and/or the second cathode active material is a polyanionic cathode active material, and wherein, prior to the first discharging and/or charging process of the sodium ion battery, the first cathode active material is fully sodiated and the second cathode active material is fully desodiated. The anode active material is pre-sodiated prior to the first discharging and/or charging process of the sodium ion battery. The invention also relates to a method for producing a sodium ion battery of this type and a use of a sodium ion battery of this type.

Description

Sodium ion battery, method for producing a sodium ion battery and use of a sodium ion battery

The invention relates to a sodium ion battery, a method for producing a sodium ion battery and the use of a sodium ion battery.

In the following, the term "sodium ion battery" is used synonymously for all terms commonly used in the prior art for galvanic elements and cells containing sodium, such as sodium battery, sodium cell, sodium ion cell, sodium polymer cell, sodium ion polymer cell and sodium ion accumulator. In particular, rechargeable batteries (secondary batteries) are included. The terms "battery" and "electrochemical cell" are also used synonymously with the term "sodium ion battery". The sodium ion battery can also be a solid-state battery, for example an inorganic, ceramic, gel-based or polymer-based solid-state battery.

In order to meet the demand for electrochemical energy storage for stationary and mobile applications, lithium-free galvanic elements or systems are increasingly coming into focus. Sodium ion batteries are a fundamentally known alternative to electrochemical storage based on lithium-containing compounds.

A sodium ion battery has at least two different electrodes, a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes has at least one active material, which is referred to as cathode active material or anode active material, respectively, optionally together with additives such as electrode binders and electrical conductivity additives, such as conductive carbon black.

A general description of sodium-ion technology can be found in Chen et al.: "Readiness Level of Sodium-Ion Battery Technology: A Materials Review" (Adv. Sustainable Syst. 2018, 2, 1700153, doi: 10.1002/adsu.201700153) and in Hasa et al.: "Challenges of today for Na-based batteries of the future: From materials to cell metrics" (Journal of Power Sources, 2021 , 282, 22872, doi: 10.1016/j.jpowsour.2020.228872). In sodium-ion batteries, both the cathode active material and the anode active material must be able to reversibly absorb or release sodium ions.

Sodium ion batteries offer a number of advantages compared to other known systems. For example, sodium ion batteries allow the use of hard carbon instead of graphite as the anode active material. Hard carbon can be produced at a lower temperature than synthetic graphite and, thanks to its mechanically more stable particles, can be calendered or compressed more than synthetic or natural graphite. In addition, a cathode active material can be used that is not based on nickel and cobalt and is inexpensive. Furthermore, sodium as an active ion, i.e. an ion that is reversibly absorbed or released, is significantly cheaper than lithium and is practically unlimitedly available. Since sodium does not alloy with aluminum, it is also possible to use current collectors or carrier foils based on aluminum instead of copper in the anode in sodium ion batteries, which significantly reduces costs. Furthermore, the materials used in sodium-ion batteries are generally more chemically stable than the components used in lithium-ion batteries and can be processed, in particular, in contact with air and moisture, which can simplify the process control in the manufacturing process, which in turn results in a reduction in costs.

In the current state of the art, sodium-ion batteries are assembled and manufactured in a completely uncharged state. This corresponds to a state in which the sodium ions are completely intercalated, i.e. stored, in the cathode, while the anode usually does not contain any active, i.e. reversibly cyclable, sodium ions.

During the first charging process of the sodium ion battery, which is also known as "formation", the sodium ions leave the cathode and are deposited in the anode. This first charging process involves complex processes with a large number of reactions taking place between the various components of the sodium ion battery.

Of particular importance is the formation of an interface between the negative active material, i.e. the anode active material, and the Electrolyte of the sodium ion battery on the anode. This interface is also referred to as the “solid electrolyte interphase” or “SEI”. The formation of the SEI, which can also be seen as a protective layer, is essentially attributed to decomposition reactions of the electrolyte with the surface of the anode active material and is sodium ion conductive.

However, sodium is required to form the SEI, which is no longer available for cycling in the charging and discharging process. The difference between the capacity after the first charge and the capacity after the first discharge, in relation to the charging capacity, is called formation loss and can be in the range of about 5 to 40%, depending on the cathode and anode active material used.

The cathode active material must therefore be oversized, i.e. provided in larger quantities, in order to achieve a desired nominal capacity of the finished sodium ion battery even after the formation loss, which increases the costs of production and reduces the specific energy of the battery. This also increases the need for potentially toxic and/or not readily available metals and compounds that are necessary for the production of the cathode active material or that arise when the cathode active material is processed, for example in recycling processes.

In the state-of-the-art cell production, the sodium-ion batteries are first assembled in an uncharged state and then formed. The formation is an extremely cost-intensive process, as it requires both special equipment and the highest safety standards, particularly with regard to fire protection, to be met.

The object of the invention is to provide a sodium ion battery that has a high specific energy and service life, as well as a cost-effective method for producing such a sodium ion battery. A further object of the invention is to implement a simplified production process for the sodium ion battery, in which in particular the pre-charge or forming process is eliminated. The "pre-charge process" in this context refers to an initial charging of the cell in order to form an SEI and ensure a stable cell voltage. The object is achieved according to the invention by a sodium ion battery with a cathode which comprises a composite cathode active material and an anode which comprises an anode active material. The composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and/or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is completely sodiated and the second cathode active material is completely deodiated before the first discharge and/or charge process of the sodium ion battery. The anode active material is pre-sodiated before the first discharge and/or charge process of the sodium ion battery.

According to the invention, a completely sodiated active material has a degree of sodification of 1 and a completely deodiated active material has a degree of sodification of 0, while a sodiated or pre-sodiated active material has a degree of sodification of greater than 0.

The term "degree of sodification" refers to the content of reversibly cyclable sodium, in the form of sodium ions, metallic sodium and/or sodium alloys, per formula unit of the active material in relation to the maximum content of reversibly cyclable sodium in the active material. In other words, the degree of sodification is a measure of what percentage of the cyclable sodium specified by the formula unit of the active material is stored or intercalated within the structure of the active material.

It goes without saying that the amount of reversibly cyclable sodium depends on the voltage range in which the sodium ion battery is to be operated. Accordingly, the formula unit of the active material can contain sodium that is not reversibly cyclable in the respective intended voltage range, even if it would be reversibly cyclable if the voltage range were expanded to comparatively higher voltages. In this case, the degree of sodification refers only to the proportion of sodium that is reversibly cyclable in the selected voltage range.

In particular, the voltage range is limited by a maximum voltage of at most 5.0 V, preferably of at most 4.5 V, particularly preferably of at most 4.3 V. For example, in a stoichiometric sodium vanadium phosphate fluoride (NVPF) with the formula unit NasV2(PO4)F3, the degree of sodiation is 1 and in the deodiated corresponding compound Na 2(PO4)Fs, the degree of sodiation is 0 when the voltage range has a maximum voltage of at most 4.3 V, in particular when the voltage range has a voltage in the range of 2.0 V to 4.3 V.

It is also possible to specify the degree of sodification in percent by multiplying the respective value of the degree of sodification by 100%. For example, a degree of sodification of 1 corresponds to a degree of sodification of 100%, a degree of sodification of 0.5 to a degree of sodification of 50% and a degree of sodification of 0 to a degree of sodification of 0%.

The formation loss occurs almost exclusively during the first discharge and/or charge process. In particular, the initial state of the cathode active material and the anode active material therefore has an influence on the prevention of formation losses.

According to the invention, the cathode has a composite cathode active material which is a combination of a completely sodiated first cathode active material and a completely deodiated second cathode active material. This combination makes it possible in a particularly simple manner, by using a blend of first cathode active material and second cathode active material, to obtain a partially deodiated composite cathode material with a desired overall degree of sodification before the first discharge and/or charging process of the sodium ion battery.

In particular, the use of only partially deodiated cathode active materials, which are complex and expensive to produce, can be dispensed with. In addition, cathode active materials that cannot be produced in a partially deodiated state can also be used in this way, while still achieving a total degree of sodification that is not equal to 0 and not equal to 1.

The term “total sodification degree” indicates the total resulting sodification degree of all components of the active material, whereby both the respective sodification degree of the components and the respective weight and Capacity share of the components in the composite cathode active material is taken into account.

The capacity proportion depends on the specific capacity of the respective cathode active materials, i.e. the specific capacity of the first cathode active material and the second cathode active material, as well as on the weight proportions of the first cathode active material and the second cathode active material in the composite cathode active material.

For example, in a composite cathode active material consisting of 50 wt.% first cathode active material and 50 wt.% second cathode active material, wherein the first cathode active material has a specific capacity twice as high as the second cathode active material, the total sodification degree S is equal to 0.33.

If the first cathode active material and the second cathode active material have the same specific capacity, the total degree of sodification of the composite cathode active material depends only on the respective weight proportion of the first cathode active material and the second cathode active material in the composite cathode active material.

For example, in this case, in a composite cathode active material consisting of 70 wt.% of first cathode active material with a sodification degree a of 1 and 30 wt.% of second cathode active material with a sodification degree b of 0, the total sodification degree S is equal to 0.7.

In other words, the total degree of sodification S in this case is the sum of the products of the weight fraction and the degree of sodification of all components of the active material.

Since the sodium ions are also incorporated into the second cathode active material after filling with electrolyte and in particular during the first discharge cycle, the ratio of the degree of sodification of the first and second cathode active material can adjust from the initial state in the composite cathode active material after filling with electrolyte and/or after the first discharge and/or charge process of the sodium ion battery. However, since the loss of formation occurs almost exclusively during the first discharge and/or charge process, the initial state of the Composite cathode active material is important for avoiding formation losses. Therefore, the information regarding the sodification levels of the first and second cathode active material in the composite cathode active material according to the invention refers to the state before the first discharge and/or charging process and in particular before filling with electrolyte.

According to the invention, the anode active material is pre-sodium-treated before the first discharge and/or charging process of the sodium ion battery. The term “pre-sodium-treated” or “pre-sodium treatment” indicates that at least some sodium is present in the structure of the anode active material, in particular adsorbed or incorporated, before the first discharge and/or charging process of the sodium ion battery.

The sodium used for pre-sodiation can be available later as a sodium reserve in the charging and discharging cycles of the sodium ion battery and can also be used to form an SEI before or during the first discharging and/or charging process of the sodium ion battery. Pre-sodiation can therefore at least partially compensate for the formation losses that would otherwise occur. In this way, the amount of expensive and possibly toxic cathode active materials or toxic compounds that may arise during the processing of the cathode active materials can be minimized and/or the energy density of the cell can be increased.

Furthermore, the reactions for the formation of the SEI do not have to take place during the first discharge and/or charging process of the assembled sodium ion battery, but can at least partially already be carried out during the production of the anode active material and/or the anode, in particular after filling the electrolyte.

By combining an at least partially deodiated composite cathode active material and an optionally substoichiometrically pre-sodium-ionized anode active material, the sodium-ion battery is at least partially charged immediately after assembly and is therefore immediately suitable for use.

The first discharge and/or charging process can therefore take place directly in the intended application, for example at the end customer. Individual Electrochemical cells can also first be connected to a battery module and only then discharged and/or charged for the first time.

In this way, the pre-charge step and the formation step, i.e. the initial charging of the sodium ion battery, can be eliminated during the manufacturing process, thereby shortening production time. In addition, the power consumption in production and the size and operation of the required production facilities are reduced.

In particular, the composite cathode active material has a total sodification degree of 0.99 or less, preferably 0.95 or less, particularly preferably 0.75 or less, further preferably 0.5 or less, before the first discharge and/or charging process of the sodium ion battery.

The composite cathode active material can further have a total degree of sodification of greater than 0, preferably of at least 0.25, particularly preferably of at least 0.5, before the first discharge and/or charging process of the sodium ion battery.

Fully deodiated cathode active materials are commercially available or can be obtained by electrochemical extraction of sodium from fully or partially sodiated cathode active materials.

Chemical extraction of sodium from fully or partially sodiated cathode active materials is also possible, in which the sodium is dissolved out using acids, for example sulfuric acid (H2SO4).

Another possibility is to obtain deodiated cathode active materials by means of solid-state synthesis or precipitation reactions.

According to the invention, the first cathode active material and/or the second cathode active material is a polyanionic cathode active material.

Polyanionic cathode active materials are known as active materials for sodium ion batteries. For the general state of the art on the use of polyanionic cathode active materials in sodium ion batteries, see for example EP 3 933 997 A1 and Hasa et al.: “Challenges of today for Na- based batteries of the future: From materials to cell metrics" (Journal of Power Sources, 2021, 282, 22872, doi: 10.1016/j.jpowsour.2020.228872).

The type of polyanionic cathode active material is fundamentally not further restricted.

Polyanionic cathode active materials are fully compatible with common electrode binders, electrolyte compositions and conductivity additives, such as conductive carbon black, as well as with common manufacturing processes of cathode active materials, such as mixing, coating, calendering, punching, cutting, winding, stacking, vacuuming, drying and lamination processes as well as electrolyte filling.

In particular, polyanionic cathode active materials with a particle size in the range from 0.1 to 35 pm can be used, preferably from 1 to 20 pm. Such particle sizes are ideal for blending the cathode active material with other particles, in particular with conductive carbon black. This makes it possible to obtain a homogeneous cathode coating mass which, after drying a carrier solvent and compaction, can be used as a composite cathode in the sodium ion battery.

Particularly preferably, the composite cathode active material consists of a first cathode active material which is a fully sodiated polyanionic cathode active material and a second cathode active material which is a fully deodiated polyanionic cathode active material.

The polyanionic cathode active material is selected in particular from the group of phosphates, sulfates, silicates and combinations thereof. Corresponding polyphosphates, polysulfates and polysilicates are included in this selection.

Preferably, the polyanionic cathode active material is selected from compounds with NASICON structure, tavorite structure, olivine structure, alluaudite structure, layered compounds and combinations thereof. Such compounds are able to reversibly absorb and release sodium ions, while the basic structure of the cathode active material is essentially retained. This reduces the stress on the cathode material during charge and discharge cycles and thus increases the service life of the sodium-ion battery.

In this context, the term “layered compounds” does not include so-called “layered oxides”, which contain oxygen anions and can be described by the general formula Na _x MO2, where M denotes a transition metal.

The polyanionic cathode active material may contain a transition metal selected from the group consisting of iron, manganese, vanadium and combinations thereof.

For example, the polyanionic cathode active material is selected from the group of compounds Nai- _x FePO4 (NFP), Naz- _x Fe3(PO4)3, Naz-xFePzO?, Nai- _x MnPO4, Naz-xMnPzO?, Naz-xMnPzO?, Naz- _x MnPO4F, Na4- _x .(Fe,Mn)3(PO ₄ )2(P2O ₇ ), Na3- _x V ₂ (PO ₄ )3 (NVP), Na ₃ ^V2(PO ₄ )2F ₃ (NVPF), Na ₃ ^V ₂ . y(VO) _y (PO4)2F3-y, Naz- _x Fez(SO4)3, Na2+2z- _X “Fe2-z(SO4)3, Na2- _x Mn2(SO4)3, Naz- _x Fez(SiO4)3, Naz- _x Mnz(SiO4)3, Naz- _x FeSiO4, Naz- _x MnSiO4 and combinations thereof, where 0 < y < 3 and 0 < z < 2, and where in the case of a fully deodiated cathode active material, x is 1, x' is 2, x“ is 3 and x“' is 4, and in the case of a fully sodiated cathode active material, x, x', x“ and x“' are 0.

It is also possible for the polyanionic cathode active material to be doped, wherein the element used for the doping partially replaces the respective transition metal present in the active material. For example, a polyanionic cathode active material containing a transition metal selected from the group consisting of iron, manganese, vanadium and combinations thereof can be doped with an element selected from the group consisting of manganese, chromium, nickel, cobalt, copper and combinations thereof.

Doping is understood to mean a content of the respective element in a proportion of not more than 5 percent by weight, based on the total weight of the polyanionic cathode active material, in particular in a proportion of not more than 1 percent by weight. In one variant, the first cathode active material is a polyanionic cathode active material and the second cathode active material is selected from the group of sodium layer oxides, sodium spinels and Prussian blue analogues (PBA).

In a further variant, the first cathode active material is selected from the group of sodium layer oxides, sodium spinels and Prussian blue analogues (PBA) and the second cathode active material is a polyanionic cathode active material.

The Prussian blue analogue is in particular selected from the group of compounds Na _x M[M'(CN)6]i- _y * z H2O, where 0 < y < 1 and z > 0, and where M and M' are each selected from the group of transition metals, preferably from the group consisting of iron, manganese, chromium, nickel, cobalt and copper. If the Prussian blue analogue is completely sodiated, x is in particular equal to 2. If the Prussian blue analogue is completely deodiated, x is in particular equal to 0.

Preferably, M and M' are each selected from the group consisting of iron, manganese and chromium. Accordingly, the Prussian blue analogue is preferably free of nickel and cobalt.

Particularly preferred is the combination of M and M' (M/M') selected from the group Fe and Fe (Fe/Fe), Fe and Mn (Fe/Mn) and manganese and manganese (Mn/Mn).

In principle, the ratio of the weight proportions of the first cathode active material and the second cathode active material in the composite cathode active material can be chosen arbitrarily.

The second cathode active material is preferably present in a proportion of 1 to 50 wt.%, based on the total weight of the first cathode active material and the second cathode active material, preferably in a proportion of 5 to 30 wt.%.

In addition to the cathode active material, the cathode may also comprise additives such as binders and electrical conductivity additives. The binder (also referred to as electrode binder) is in particular selected from the group consisting of polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), cellulose, acrylates (for example polymethyl methacrylate), polyvinylpyrrolidone (PVP), styrene-butadiene rubber (SBR), polyisobutene (PIB), polyethylene (PE), polypropylene (PP) and mixtures thereof.

The electrical conductivity additive (also referred to as electrical conductivity additive) can be selected from the group consisting of conductive carbon black, carbon nanotubes (CNT), graphene, graphite, expanded graphite and carbon nanofibers, porous carbons (as described, for example, in EP 2 528 879 B1 and DE 10 2013 106 114 A1), gas-phase produced carbon nanofibers (also referred to as “VGCF” for English “vapour grown carbon fibers”) and combinations thereof.

The anode active material can be selected from the group consisting of hard carbon, soft carbon, synthetic graphite, natural graphite, graphene, mesocarbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof.

The Prussian blue analogue in the anode active material can be selected analogously to the Prussian blue analogues described for the composite cathode active material, but where 0 < x < 2.

Hard carbon is particularly preferred as the anode active material.

In particular, the hard carbon can be a hard carbon that has been manufactured industrially from renewable materials through appropriate carbonization. Such hard carbon types are sold, for example, by Stora Enso under the name Lignode®.

In particular, the anode active material is pre-sodium-treated to such an extent that more sodium is present before the first discharge and/or charge process of the sodium ion battery than is required to form the SEI during the anode manufacture and/or the formation of the sodium ion battery. Preferably, the anode active material has a degree of sodification of greater than 0 and additionally a stable SEI before the first discharge and/or charging process of the sodium ion battery.

The anode active material is pre-sodium-stoichiometrically pre-sodium-containing, particularly before the first discharge and/or charging process. This means that the degree of sodium-containing of the anode active material is particularly less than 1.

In particular, the degree of sodification of the anode active material before the first discharge and/or charge process can be in the range from 0.01 to 1, preferably in the range from 0.05 to 0.6, particularly preferably from 0.1 to 0.5.

If the anode active material already contains sodium, which cannot participate in the cyclization because it cannot be extracted electrochemically, i.e. is not active sodium, this proportion of sodium is not considered to be a component of the pre-sodium treatment according to the invention.

In addition to the anode active material, the anode can have further components and additives, such as a carrier, a binder and/or an electrical conductivity additive. All conventional compounds and materials known in the prior art can be used as further components and additives, as well as the compounds already described for the cathode.

Preferably, the anode active material is pre-sodium-treated before the first discharge and/or charging process of the sodium ion battery to such an extent that the sodium ion battery has a state of charge (SoC) in the range from 1 to 100%, preferably from 5 to 60%, particularly preferably from 10 to 50%, before the first discharge and/or charging process.

The SoC indicates the remaining available capacity of the sodium ion battery in relation to the maximum capacity of the sodium ion battery and can be easily determined, for example, via the voltage and/or current flow of the sodium ion battery.

The amount of sodium that must be used for pre-sodiation of the anode active material to achieve a certain SoC before the first discharge and/or charge process of the sodium ion battery depends on whether an SEI has already been formed on the anode active material before the first discharge and/or charging process of the sodium ion battery. If no SEI has yet been formed on the anode active material, the anode active material should be pre-sodium-treated to such an extent that the added sodium is sufficient both to form the SEI and to achieve the corresponding capacity of the sodium ion battery. The amount of sodium required to form the SEI can be estimated based on the anode active materials used.

The SoC of the sodium-ion battery before the first discharge and/or charge process can be adjusted not only by the pre-sodiation of the anode active material, but also by the total sodification degree of the composite cathode active material.

The total sodification degree of the composite cathode active material can be adapted to the pre-sodiation of the anode active material. In other words, the total sodification degree of the composite cathode active material can be reduced by the amount of sodium used for the pre-sodiation of the anode active material. In this way, the energy density or the open cell voltage of the sodium ion battery is further optimized.

The anode active material can also be pre-sodium-treated to such an extent that an excess of sodium results in the sodium-ion battery, but at the same time a SoC is present in the aforementioned ranges before the first discharge and/or charge process of the sodium-ion battery. An excess of sodium can serve to improve the service life of the sodium-ion battery.

Between the cathode and the anode, the sodium ion battery according to the invention has a separator which separates the two electrodes from each other, i.e. the cathode and the anode.

The separator is permeable to sodium ions but non-conductive to electrons.

Polymers can be used as separators, in particular a polymer selected from the group consisting of polyesters, in particular polyethylene terephthalate, polyolefins, in particular polyethylene and/or polypropylene, polyacrylonitriles, polyvinylidene fluoride, polyvinylidene Hexafluoropropylene, polyetherimide, polyimide, aramid, polyether, polyetherketone, synthetic spider silk (as described, for example, in DE 10 2018 205484 A1) or mixtures thereof. The separator can optionally be additionally coated with ceramic material, for example with SiC>2 or AI2O3.

In addition, the sodium ion battery has an electrolyte that is conductive for sodium ions and that can be either a solid electrolyte or a liquid that includes an electrolyte solvent and at least one sodium conducting salt dissolved therein, for example sodium hexafluorophosphate (NaPFe). Other possible sodium conducting salts can be: sodium triflate (NaCFsSCh), sodium tetraborate (NaBF4), sodium bis(trifluoromethylsulfonyl)amide (NaTFSI), sodium bis(trifluoromethylsulfonyl)amide (NaFSI), sodium bis(oxalato)borate (NaBOB).

The electrolyte solvent is preferably inert. Suitable electrolyte solvents are, for example, organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), sulfolane, 2-methyltetrahydrofuran, acetonitrile and 1,3-dioxolane.

In a variant, two or more of the above liquids can be used.

Preferred sodium conducting salts are sodium salts which have inert anions and which are preferably non-toxic. Suitable sodium salts are in particular sodium hexafluorophosphate (NaPFe), sodium tetrafluoroborate (NaBF4) and mixtures of these salts.

If the electrolyte is liquid, the separator is particularly soaked or wetted with the electrolyte.

The object of the invention is further achieved by a method for producing a sodium ion battery, comprising the following steps: A composite cathode active material is provided by mixing a first cathode active material and a second cathode active material, wherein the first cathode active material and/or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is completely sodiated and the second cathode active material is completely deodiated. An anode active material is provided. The composite cathode active material is installed in a cathode and the anode active material is installed in an anode and the cathode and the anode are assembled into a sodium ion battery. The anode active material is pre-sodiated before or after the anode active material is installed in the anode.

The individual components of the sodium ion battery produced in the process according to the invention are made in particular from the materials previously described for the sodium ion battery according to the invention.

Accordingly, the sodium ion battery according to the invention described above is obtainable in particular by the process according to the invention.

According to the invention, the composite cathode active material is obtained by mixing the first and second cathode active materials. In other words, the composite cathode active material is in particular a blend of first cathode active material and second cathode active material. A composite cathode active material with a desired overall degree of sodification can thus be obtained particularly easily.

The pre-sodium plating of the anode active material can be carried out in particular by the techniques known in the prior art for the production of sodium-containing active materials.

For example, a mixture of the anode active material with metallic sodium can be produced. The mixture of anode active material can be stored for a period of up to two weeks, preferably up to one week, particularly preferably up to five days. During this period, the sodium can be incorporated into the anode active material so that a pre-sodium-treated anode active material is obtained.

In one variant, the pre-sodium plating of the anode active material can be carried out by mixing the anode active material with a sodium precursor and subsequently converting the sodium precursor to metallic sodium. In a further variant, the pre-sodium plating of the anode active material can be carried out by injecting sodium into the anode active material and/or the anode.

In a further variant, the pre-sodium plating of the anode active material can be carried out by vapor deposition of sodium onto the anode active material and/or the anode.

By storing the anode in an electrolyte for a predetermined period of time, for example 2 minutes to 14 days, a stable SEI can be built up on the anode.

Finally, it is possible to pre-sodinate the anode active material by electrochemically treating the anode active material built into an anode in a sodium-containing electrolyte. In this way, the SEI can be formed on the anode during pre-sodiation. By storing the anode in the electrolyte, the SEI can be further completed and kinetically stabilized.

In order to produce a sodium-ion battery that is ready for immediate use, the sodium-ion battery can have a state-of-charge (SoC) in the range of > 1% immediately after the assembly step, before a first discharge and/or charging process of the sodium-ion battery.

The object of the invention is further achieved by the use of a sodium ion battery as described above in a vehicle, a stationary energy storage device or a portable device. The portable device can in particular be a smartphone, a power tool, a tablet or a wearable. The sodium ion battery is preferably used in a vehicle, for example a hybrid or electric vehicle.

Further advantages and characteristics of the invention will become apparent from the following description and examples, which are not to be understood in a limiting sense.

Beispiel 1 (Referenzbeispiel) Table 1 lists the substances and materials used in the examples. Table 1: Substances and materials used.

Example 1 (reference example)

A mixture of 94 wt.% sodium iron phosphate (NaFePO4, NFP), 3 wt.% PVdF, and 3 wt.% conductive carbon black is suspended in NMP at 20 °C using a high-shear dissolver mixer. A homogeneous cathode coating mass is obtained, which is doctored onto an aluminum carrier foil rolled to a thickness of 15 pm. After stripping off the NMP, a composite cathode film with a surface weight of 19.5 mg/cm ² is obtained.

Analogously, an anode coating mass with a composition of 94 wt.% hard carbon, 2 wt.% SBR, 2 wt.% CMC and 2 wt.% Super C65 is produced and applied to a 15 pm thick rolled aluminum carrier foil. The anode film produced in this way has a basis weight of 5.7 mg/cm ² .

The cathode with the cathode film is assembled using an anode with the anode film, a separator (thickness: 25 pm) made of polypropylene (PP) and a liquid electrolyte of a 1 M solution of NaPFe in EC/DMC (3:7 w/w) to form an electrochemical cell with 25 cm ² active electrode area, which is packaged and sealed in high-quality aluminum composite foil (thickness: 0.12 mm). The result is a pouch cell with external dimensions of approximately 0.5 mm x 6.4 mm x 4.3 mm.

The cell is first charged to 3.5 V (C/10) and then discharged with C/10 to 2.0 V.

The capacity of the first charge is 52.5 mAh and the capacity of the first discharge is 38.5 mAh. This results in a formation efficiency of about 73.3% for the complete cell, which means a formation loss of about 26.7%.

Example 2 (Sodium ion battery according to the invention)

A mixture of 65.8 wt.% sodium iron phosphate (NaFePO4), 28.2 wt.% FePO4, 3 wt.% PVdF, and 3 wt.% conductive carbon black is suspended in NMP at 20 °C using a high shear mixer. A homogeneous cathode coating mass is obtained which is applied to a rolled sheet with a thickness of 15 pm. The aluminum collector carrier foil is doctored out. After removing the NMP, a cathode film with a surface weight of 19.5 mg/cm ² is obtained.

Analogously, an anode coating mass with a composition of 94 wt.% hard carbon, 2 wt.% SBR, 2 wt.% CMC and 2 wt.% Super C65 is produced and applied to a 15 pm rolled aluminum collector carrier foil. The anode film produced in this way has a basis weight of 7.5 mg/cm ² .

This anode film is pre-sodium-treated with 30.8 mAh of sodium before cell assembly. Approximately 15.7 mAh of sodium builds up a SEI protective layer and approximately 15.1 mAh of sodium remains as cyclable sodium in the hard carbon.

30.8 mAh of sodium corresponds to approximately 1.15 mmol or approximately 26.5 mg of sodium.

The cathode with the cathode film is assembled using an anode with the anode film, a separator (25 pm) and an electrolyte of a 1 M solution of NaPFe in EC/DMC (3:7 w/w) to form an electrochemical cell with 25 cm ² electrode area, which is packaged and sealed in aluminum composite foil (thickness: 0.12 mm). This results in a pouch cell with external dimensions of approximately 0.5 mm x 6.4 mm x 4.3 mm.

After dosing the electrolyte and final sealing of the cell according to the invention, it has an open voltage of approx. 2.3 to 2.9 V, which results from the potential difference between the partially deodidized cathode and the pre-sodium-ionized anode. The nominal capacity of the sodium ion battery is 50.4 mAh, so that the sodium ion battery has a state of charge (SoC) of 30% immediately after production.

The cell is initially charged to 3.5 V (C/10) and then discharged with C/10 to 2.0 V. Since the cell already has a SoC of 30% after assembly and activation with liquid electrolyte, a charge of 35.3 mAh is observed during further formation with C/10, while the first C/10 discharge is at 50.4 mAh.

The sodium ion battery according to the invention accordingly has a 31% higher nominal capacity with an identical total cathode load and a 32% higher anode load compared to the reference example. In a further embodiment, the anode loading could alternatively be kept constant compared to the reference example and the cathode loading reduced, resulting in a similar nominal capacity, but with significantly reduced use of cathode material. Since an anode with pre-sodium-dioxide anode active material and partially de-sodium-dioxide composite cathode active material is used to produce the sodium ion battery, the sodium ion battery according to the invention can be used immediately after the production step.

Claims

patent claims 1. Sodium ion battery with a cathode comprising a composite cathode active material and an anode comprising an anode active material, wherein the composite cathode active material comprises at least a first cathode active material and a second cathode active material, wherein the first cathode active material and/or the second cathode active material is a polyanionic cathode active material, wherein the first cathode active material is completely sodiated and the second cathode active material is completely deodiated before the first discharge and/or charge process of the sodium ion battery, and wherein the anode active material is pre-sodiated before the first discharge and/or charge process of the sodium ion battery. 2. Sodium ion battery according to one of the preceding claims, wherein the polyanionic cathode active material is selected from the group of phosphates, sulfates, silicates and combinations thereof. 3. A sodium ion battery according to claim 2, wherein the polyanionic cathode material is selected from compounds having NASICON structure, tavorite structure, olivine structure, alluaudite structure, layered compounds and combinations thereof. 4. A sodium ion battery according to claim 2 or 3, wherein the polyanionic cathode material contains a transition metal selected from the group consisting of iron, manganese, vanadium, and combinations thereof. 5. Sodium ion battery according to one of the preceding claims, wherein the second cathode active material is present in a proportion of 1 to 50 wt.%, based on the total weight of the first cathode active material and the second cathode active material, preferably in a proportion of 5 to 30 wt.%. 6. Sodium ion battery according to one of the preceding claims, wherein the anode active material is selected from the group consisting of hard carbon, soft carbon, synthetic graphite, natural graphite, graphene, Mesocarbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof. 7. Sodium ion battery according to one of the preceding claims, wherein the anode active material is pre-sodium-treated before the first discharge and/or charge process of the sodium ion battery to such an extent that the sodium ion battery has a state of charge (SoC) in the range from 1 to 100%, preferably from 5 to 60%, particularly preferably from 10 to 50%, before the first discharge and/or charge process. 8. A method for producing a sodium ion battery, comprising the following steps: - Providing a composite cathode active material by mixing a first cathode active material and a second cathode active material, wherein the first cathode active material and/or the second cathode active material is a polyanionic cathode active material, and wherein the first cathode active material is fully sodiated and the second cathode active material is fully deodiated; - Providing an anode active material; - incorporating the composite cathode active material in a cathode and the anode active material in an anode; and - Assembling the cathode and the anode to form a sodium ion battery; wherein the anode active material is pre-sodium-treated before or after the anode active material is installed in the anode. 9. The method according to claim 7, wherein the sodium ion battery has a state of charge (SoC) in the range of > 1% immediately after the assembly step, before a first discharge and/or charging process of the sodium ion battery. 10. Use of a sodium ion battery according to one of claims 1 to 7 in a vehicle, a stationary energy storage device or a portable device.